Southerners also had to swear an oath to follow laws that dealt with what issue?

The 15th Amendment, which sought to protect the voting rights of African American men after the Civil War, was adopted into the U.S. Constitution in 1870. Despite the amendment, by the late 1870s discriminatory practices were used to prevent Black citizens from exercising their right to vote, especially in the South.

cornfield (filler filler filler filler ignore this filler filler)

the answer is a) high entry costs